1. Field of the Invention
The present invention relates to a photographic printer for exposing and printing on a light-sensitive material an image recorded on a photographic film, and in particular to a photographic printer which is capable of accurately and easily controlling the amount of light reaching each of a plurality of small regions of a light-sensitive material so as to perform density compensation, color compensation and the like.
2. Description of the Related Art
An example of an apparatus for exposing and printing on a light-sensitive material an image recorded on a photographic film is disclosed in Japanese Patent Publication (Kokoku) Sho. 52-20853. In that apparatus, light is projected onto a photographic film on which an image is recorded, and a liquid crystal cell is disposed in the middle of the path of light which has passed through the photographic film. A voltage supplied to the liquid crystal cell is controlled for adjusting the amount of light which forms an image on the light-sensitive material. Also, Japanese Patent Publication (Kokoku) Sho. 64-10819 discloses an apparatus provided with a light source for illuminating an image recorded on a photographic film, and a liquid crystal cell which is disposed between the light source and the photographic film and which includes liquid crystal elements arranged in a matrix. Voltages supplied to the liquid crystal elements are varied to change the amount of light passing through each of the liquid crystal elements, whereby density compensation, color compensation, and the like are carried out for an image exposed on a light-sensitive material.
The apparatus disclosed in Japanese Patent Publication (Kokoku) Sho. 64-10819, however, has the drawback that in order to change the transmittance of the liquid crystal cell, the layer of liquid crystal must be composed of a twisted-nematic liquid crystal or bistable ferroelectric liquid crystal, and a polarizing plate must be disposed on each of the front side (the side facing the light source) and the back side of the layer of liquid crystal. Accordingly, a major part of the light is lost at the polarizing plates and the layer of liquid crystal before reaching the light-sensitive material. The intensity of light forming an image on the light-sensitive material therefore becomes very low compared to that of the light projected on the liquid crystal cell, which brings about a problem that the time required for proper exposure is prolonged.
The above-described apparatus also has the drawback that when the intensity of the light is increased for compensating for the loss of light, polarized light which does not pass the polarizing plates is converted to heat. As the heat accumulates, the temperature of the layer of liquid crystal is elevated, which causes changes in the transparency and hue of the liquid crystal due to the temperature-dependent characteristics of the liquid crystal. In the case where the polarizing plates are of a widely used type in which a base material made of polyvinyl alcohol (PVA) is laminated with triacetyl cellulose (TAC), about 60% of the light is absorbed by the first polarizing plate and about 15% by the second polarizing plate. The absorbed light wastefully changes to heat.
The decrease in the amount of light passing through the liquid crystal cell causes the problems that the time required for exposure becomes long and that a stronger illumination source is needed. Therefore, conventional photographic printers are not satisfactory in terms of printing capacity and consumption of electric power.